Add the ability to set the fallocate_reserve value as a percentage.
This happens automatically when adding the '%' at the end of the value.
Having the ability to set a % of free space rather than a byte value is
useful especially when drive sizes are heterogenous.
The default for fallocate_reserve has been adjusted to 1%, having the
fallocate_reserve set seems sensible for all deploys and percentages are
far safer to default than byte values (across drives of any size).
Tests added for using fallocate_reserve as a percentage.
Duplicate tests for fallocate_reserve have been removed.
Docs updated to reflect the fallocate_reserve change.
Change-Id: I4aea613a708205c917e81d6b2861396655e73238
0da9da5131